The present invention relates to a film carrier for endodontic dental radiographs in the parallel method, comprising a bite-on block, a back plate for mounting a dental X-ray film shaped onto said block and at right angles to the bite-on plane formed by said block, a guide rod held by means of a detachable plug-in fastening to the bite-on block and a sighting ring displaceable on the guide rod in its longitudinal direction and having a mounting support for fixing the film carrier to a cone of a dental X-ray examination unit.
In endodontia, for the purpose of showing a tooth, dental radiographs are made using X-ray examination units which are constructed for dental purposes. The linear measurement of the root canal being of great importance in endodontia. This linear measurement is determined with the aid of dental radiographs. The parallel method is the ideal way of taking test radiographs. In this X-ray recording method the central beam is directed at right angles onto the tooth axis and the film plane. Dental X-ray films have been developed for intraoral shots, which have a plate-like construction and standardized dimensions, so that the film can be introduced into the oral cavity. As a function of the position of the particular tooth which is to be photographed, the dental X-ray film plate is held by the patient in the each case necessary position following insertion into the mouth. This is brought-about by pressing the film by means of the thumb or index finger against the object to be photographed.
A film carrier with the aforementioned features has been developed more particularly for the use of the parallel method enabling the film to be introduced in such a way into the patient's mouth, that it is parallel to the longitudinal axis of the tooth. Due to the space conditions in the mouth, at certain points the film must be at a greater distance from the tooth and in order that this does not lead to distortions, it is necessary to increase the focus-film difference, which is effected by means of the extended cone on the X-ray tube, i.e. on the X-ray examination unit.
In the case of such film carriers, the film is held on a back plate, onto which is shaped a biting plate, by means of which the patient holds the film carrier by tooth pressure.
However, such film carriers are not suitable for test photographs with root canal instruments and/or cofferdam. Therefore, in general, endodontic photographs are produced by using the half-angle method, which is an X-ray recording method in which the central beam on the apex is directed at right angles to the angle bisector between the film plane and the tooth axis. However, this half-angle method often leads to unsatisfactory results, which applies both for the linear measurement of the root canal and for the reproducibility, because it is difficult to compare the different control photographs of a root treatment. In addition, the biting plates arranged centrally with respect to the film carrier back plate are so dimensioned and so arranged on the back plate, that it is not possible to use root canal instruments, because the needles used for preparing the root canal remain in the latter during radiography. The gripping end of said needles project from the root canal and come to rest in such a way in the vicinity of the biting plate of a film carrier inserted in a patient's mouth, that conventional film carriers cannot be used. In addition, the film carrier back plates have smaller dimensions than the dental X-ray films used, so that said film projects by a portion over the all-round edge to the back plate and as a result during radiography the film is bent by pressure action. A folding over or bending of the dental film leads to small electric discharges in the emulsion layer of the film, which can be revealed in the form of black lines on the developed film and can give rise to misinterpretations. Moreover, when biting together the teeth, the patient is subject to a pressure pain caused by the upper edge of the film introduced by means of the film carrier into the patient's mouth and whose relatively sharp edges come into contact with the sensitive mucous membranes of the gum and as a result of the marked pressure action causes pain. The patient often tends to escape the pain by reducing the biting pressure, which can in turn lead to a positional displacement of the film, although it is held in the film carrier.
Furthermore, film carriers for endodontic dental radiographs are known in numerous different forms. Thus, the film carrier according to US Pat. 4,593,401 comprises an approximately U-shaped moulded body which, in its web connecting the two legs is provided with a slot-like reception opening, which serves to receive the dental X-ray film. The film is secured in such a way that a small portion thereof is inserted into said slot-like recess in the carrier and is held therein. However, this film carrier does not solve the problem of bending, folding over and the like of the film, because there is no full-area engagement of said film on the mounting support. Moreover, this film carrier does not permit test radiographs in the upper jaw and radiographs using the parallel method.
U.S. Pat. No. 4.592.084 discloses a further film carrier with a biting plate, in which no back plate is provided for receiving the dental X-ray film. The film carrier is constructed as a U-shaped clamping holder securing a portion of the film. That region of the dental X-ray film which is not held by the film carrier clamp is unprotected, so that a bending and positional change to the film is possible, which can lead to inaccurate radiographs.